There have been active studies on estimation of human posture based on a captured moving image data. A posture estimation apparatus can determine person's motions from a moving picture through computer analysis and thus can perform behavior analysis without involving manual works. Applications of behavior analysis include detection of unexpected behaviors on the street, analysis of in-store purchase behaviors, aid in work efficiency improvement at a factory, and form coaching in sports, for instance.
When estimating a human posture, it is desirable that estimation of part posture be possible, for instance. Here, the “part” refers to a component of an articulated object (e.g., head, trunk, arm and leg). The “part posture” refers to a position or angle of the part in human posture. Since a person changes part posture by motion, if the position of the part can be estimated, it is possible to estimate motion, that is, what this person is doing or what the person is going to do from now on.
Such human posture estimation is preferably performed without attaching any apparatus such as an azimuth sensor to the person. This is because an estimation technique requiring attachment of an apparatus to a person has a difficulty in handling an unspecified person as a subject of estimation and will incur more cost when there are many subjects of estimations.
PTL 1 discloses a technique of estimating a person's posture based on an image of the person captured
The technique described in PTL 1 (hereinafter referred to as “related art 1”) determines a center of gravity of a person's silhouette from a captured image, calculates a distance from the center of gravity to each point on a contour of the person's silhouette, detects a vertical axis that extends upward from the center of gravity and assumes a point of intersection with the contour of the person's silhouette as a vertex of the head. Related art 1 searches for a point at which the distance calculated counterclockwise with the vertex the head as a start point becomes a maximum, determines a point at which the distance first becomes a maximum as a tip of the right hand and determines points at which the distance next becomes a maximum as tips of the right leg, left leg and left hand. According to this related art 1, it is possible to estimate a person's posture without attaching any apparatus such as an azimuth sensor to the person.
For example, PTL 2 describes a technique of estimating a person's posture based on an image of the person captured.
The technique described in PTL 2 (hereinafter referred to as “related art 2”) takes pictures of a person wearing clothes in color other than blue and varying from one part to another against a blue background. Thus, related art 2 acquires the person's silhouette based on a difference in color information between the background image and the person's image and detects the person's part from color information of the clothes. Using this related art 2, it is possible to estimate a person's posture without attaching any apparatus such as a sensor to the person.